Labour conditions, hence productivity and quality of assembly depend on mass, size, reliability and vibration level of an impact wrench.
An important part of an impact wrench is a hammer which transforms energy of a power drive into the work of tightening a threaded joint so as to ensure high labour productivity and desired tightening force.
An impact wrench is known in the art (SU, A, No. 180147), comprising a casing accommodating a rotatable anvil having a portion for the attachment of a socket wrench and a shaft coupled to a drive and supporting a hammer mounted to perform rotation and axial movement between two positions. Impact jaws are provided on the surfaces of the hammer and anvil facing towards one another, which engage one another in one of the hammer positions. The impact wrench also has a spring which is mounted in the casing coaxially with the shaft and cooperates with the hammer for moving it into the position, in which the hammer and anvil engage each other.
As the hammer must have a substantial mass which determines tightening torque of a threaded joint, vibrations of the impact wrench, which is so constructed, are very high because of the axial movement of the hammer, and this also entails unproductive energy consumption of the drive.
An impact wrench having a lower level of vibrations is also known in the art (U.S. Pat. No. 2,753,965). This impact wrench comprises a casing accommodating a rotatable anvil having a portion for the attachment of a socket wrench and a shaft coupled to a drive and supporting a hammer which has a body having one end thereof facing towards the anvil, an axial passage and at least two longitudinally extending passages, each accommodating a pin mounted to perform reciprocations between two positions, the pin being engaged with the anvil in one of these positions and having a bearing surface engageable, during the pin movement into the other position, with a respective bearing surface of a driving member which is coupled to the shaft to perform rotation and axial movement between two positions and which is connected to the hammer body for combined rotation, the driving member cooperating with a spring to move the driving member into a position, in which the pins are engaged with the anvil. The hammer body and driving member are mounted in tandem on the shaft. The driving member is guided by the shaft during movement. The driving member is in the form of a plate having two openings at the opposite ends thereof. The plate is rigidly connected to a hub for mounting the driving member on the shaft. The hammer body has an axial passage and two longitudinally extending passages parallel therewith. The axial passage diameter is determined by the diameter of the shaft, and the diameter of the longitudinally extending passage is determined by the diameter of the pin received therein, which diameter is chosen in accordance with the pin strength requirements depending on impact load. The distance between these passages is about equal to the pin diameter. It depends on the distance between the openings in the plate as one end of each pin is received in a respective opening of the plate. An annular groove is made at this end of the pin. The pin diameter at this point is equal to the width of the plate opening. One end face of the groove is a bearing surface engageable with one of the plate surfaces when the pin is moved into a position in which it is engaged with the anvil, the other end face of the groove being the other bearing surface of the pin engageable with the other surface of the plate when the pin moves into the other position.
This structural arrangement of the hammer, in which the driving member and the hammer body are mounted in tandem on the shaft results in their relative misalignment in operation and jamming, since the driving member is guided by the shaft and the pins are guided by the hammer body. Consequently, the pins are misaligned and jammed between the hammer body and bearing surfaces of the driving member.
In addition, misalignment of the driving member may cause breakage of the pins in the annular grooves.
All this constitutes the reason for failure of the impact wrench, lowers its reliability in operation and reduces service life.
The mass and size of the hammer and, in particular, of the hammer body are large enough since the distance between the openings of the driving member plate in which the pin ends are received should be greater than the overall dimension of the driving member hub, so that the size and mass of the impact wrench increase.